1. Field of the Invention
The present invention relates to a technique of shortening a readout time in an image sensor having a plurality of pixels arranged in a matrix topology in the horizontal and vertical directions.
2. Description of the Related Art
In recent years, along with an increase in number of pixels of an image sensor, it is necessary to ensure a given frame rate. To do this, the pixels of an image sensor, the number of which has been increased, need to be thinned out and then read out. If, however, the pixels are thinned out and then read out, the image quality drops due to a loss of the information of pixels.
To solve such problem, Japanese Patent Laid-Open No. 2005-244995 has proposed a method in which pixels with the same color are connected to an output circuit, added, and then read out.
The conventional technique, however, suffers the following problem. That is, in Japanese Patent Laid-Open No. 2005-244995, it is possible to add only two pixels. In order to further shorten a readout time, there is no choice but to thin out and then read out pixels, thereby deteriorating the image quality.